Mark any SDHCI controllers that aren't registered by the board files as
disabled in the device-tree files.

In practice, these controllers:

* Have nothing hooked up to them at all, or
* For ports intended for SDIO usage, the drivers for anything that might
  be attached are not in the device-tree yet. If/when drivers appear, the
  SD/MMC port can be re-enabled.

The only possible exception is TrimSlice's mico SD slot, but that wasn't
enabled in the board files before anyway, and doesn't work when all the
SDHCI controllers are enabled anyway.
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NOlof Johansson <olof@lixom.net>